Adults with recent onset and long-duration symptomatic, ketosis resistant diabetes mellitus and with borderline abnormalities of glucose tolerance were studied with oral and intravenous glucose tolerance tests, arginine infusions and circulating mononuclear cell insulin receptor assays. Subjects were then placed on a weight reduction diet. They were restudied every 5 weeks to determine the degree of reversibility of changes in glucose tolerance and gluco-regulatory hormones and in diabetes.